Apparatus for the measurement of dust content a gas stream

ABSTRACT

Aparatus for measuring and/or regulating the dust content of a gas stream comprising a conveyor pipe through which the gas stream is arranged to pass and a pair of tubes extending from the walls of the conveyor pipe and being substantially diametrically opposed, one of the tubes containing a radiation emitter, a foil between the emitter and the conveyor pipe and a nozzle between the foil and the conveyor pipe and the other of the tubes containing a receiver, a foil between the receiver and the conveyor pipe and a nozzle between the foil and conveyor pipe, said nozzles being adapted to be connected to a compressed gas source.

United States Patent Stiinner et al.

[ Nov. 13, 1973 APPARATUS FOR THE MEASUREMENT OF DUST CONTENT A GAS STREAM 2,912,943 11/1959 Nicolai et al. 110/104 3,291,981 12/1966 Stock 250/43.5 D 3,353,021 11/1967 Stewart 250/43.5 D 3,412,699 11/1968 Culp et al. 250/42.5 D

Primary Examiner-Kenneth W. Sprague Att0rneyHolman & Stern [57] ABSTRACT Aparatus for measuring and/or regulating the dust content of a gas stream comprising a conveyor pipe through which the gas stream is arranged to pass and a pair of tubes extending from the walls of the conveyor pipe and being substantially diametrically opposed, one of the tubes containing a radiation emitter, a foil between the emitter and the conveyor pipe and a nozzle between the foil and the conveyor pipe and the other of the tubes containing a receiver, a foil between the receiver and the conveyor pipe and a nozzle between the foil and conveyor pipe, said nozzles being adapted to be connected to a compressed gas source.

7 Claims, 2 Drawing Figures PATENTEUNHY 13 7975 APPARATUS FOR THE MEASUREMENT OF DUST CONTENT A GAS STREAM BACKGROUND OF THE INVENTION This invention relates to apparatus for the measurement and/or regulation of the dust content of a gas stream with the aid of a radiation emitter arranged on one side of a conveyor pipe and a receiver arranged on the other side of the conveyor pipe.

ln coal-dust-fired boiler installations, a fuel-air mixture is fed to the boiler through several burner pipes, with pit coal dust or lignite dust being predominantly used as fuel. The fuel is normally crushed in mills and then conducted through a wind-Sifter installation. The wind sifter has the task of feeding only a specific grain size range to the burner, while excessively large dust particles are conveyed back to the mills.

PRIOR TECHNIQUES The main problem of such coal-dust firing systems consists in maintaining a specific ratio of coal-dust to air. To this end, distributor devices have been developed which consist essentially of a distributor hopper, a conveyor belt running at variable speed and a heapheight regulation system. Since the coal dust can contain greatly fluctuating quantities of water, there is the danger that bridges may form in the distributor hopper and that the distribution may become irregular. How I ever, a boiler can be operated with optimum efficiency only if the coal-dust-air mixture of all burner pipes is constant within close tolerances and the quantity of dust per unit of time is equal for all pipes. Moreover, deviations from the ideal ratio can lead to serious damage to the boiler.

Hitherto, no continuous measurement method has become known with which it would be possible constantly to monitor and regulate the dust density or the dust quantity per unit of time in the individual burner conduits. Measurements have heretofore been limited to mechanical measurements of random sample type, which are very costly for labor and cannot be carried out without interference with the normal boiler working. Moreover, very great defects are associated with the known mechanical measurement methods.

SUMMARY OF THE INVENTION The object of the invention is to provide a continuous measurement method which requires no great maintenance expense and delivers regulating pulses which influence the coal dust distributor or the air supply.

A further object of the invention provides apparatus for measuring and/or regulating the dust content of a gas stream, said apparatus comprising a conveyor pipe through which said gas stream is arranged to pass, a pair of tubes extending from the walls of said conveyor pipe and being substantially diametrically opposed, a radiation emitter located in one of said tubes and a receiver located in the other of said tubes, a pair of foils and a pair of nozzles, each of said tubes being divided into two portions by a foil and the portions of each tube between the foil and said conveyor pipe having a nozzle extending into said tube, each of said nozzles being adapted to be connected to a compressed gas source.

According to another object of the invention, at least the tube section lying between the emitter and foil is monitored by a light barrier which responds after any damage to the foil as a result of penetration by dust and trips an alarm system. The same monitoring system can be used for the protection of the ray receiver, especially an ionisation chamber.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows diagrammatically in longitudinal section, one embodiment of an apparatus according to the invention; and

FIG. 2 is an enlarged section of the area A indicated in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, the apparatus comprises a conveyor pipe 1 which can be inserted at a convenient point in a burner conduit. The conveyor pipe 1 has a constriction after the style of a Venturi tube, which serves to homogenize the dust-air mixture at the measurement cross-section. The ray passage takes place at the position of the minimum cross-section. This has the further advantage that a relatively weak radioactive emitter can be used.

The conveyor pipe 1 is provided at the point of ray passage with openings 2 and 3 into which tubes 4 and 5 are set. Foils 6 and 7 are stretched in these tubes and tightly seal off the tube cross-section. The tube sections between the foils 6 and 7 and the conveyor pipe 1 are designated by 4a and 5a. In these tube sections, in the immediate vicinity of the foils, there are installed nozzles 8 and 9 which are in communication through conduits with a compressed gas source, preferably compressed air. The air supply takes place through a combination of annular and slot-type nozzles which impart a certain twist to the issuing air. The speed of issue of the air at the nozzle openings must not exceed a certain value, since otherwise air and dust could be sucked from the lateral conveyor pipe.

In FIG. 2, a part of the nozzle Q is illustrated .on a larger scale. The air enters in the direction of the arrow through a supply conduit 20 and is conducted by way of nozzle bores 21 and 22 extending in specific threedimensional directions to an annular nozzle 23.

At the end of the tube section 4b there is secured a radioactive emitter 10 provided with screening. The end of the tube section 5b carries a ray receiver 11 which is preferably formed as an ionization chamber.

The tube section 4b is provided with two opposite short tubes in which a light source 12 and a photoelectric cell 13 are accommodated. The photo-electric cell 13, which can also be replaced by a photo-diode or by a photo-transistor, charges an amplifier 14, the output of which is connected with a relay 15. The contact 16 of this relay is in the circuit of an alarm system (not shown). This contact can be used at the same time, through a servo drive system, to actuate a slider 17 which tightly seals off the radioactive emitter 10. A similarly constructed light barrier with a light source 18 and a photo-electric cell 19 is installed in the tube section 5b.

The apparatus as described has the following manner of operation:

The coal-dust-air current flowing through the conveyor pipe 1 in the direction of the arrow attenuates the radiation issuing from the radioactive emitter l0 and arriving at the receiver 11, by an amount which is substantially dependent upon the coal dust density. Thus, if the velocity and the density of the air fed to the burner are known, the amplified current of the receiver is a measure of the quantity of coal dust conveyed per unit of time or for the ratio of coal dust air. The actual value of the receiver current can be fed, after comparison with a desired value, to a regulating circuit in which the quantity of coal dust or air is varied in the case of deviations from the desired value. Of course, it is also possible merely to indicate the measured value and to leave any necessary interventions to the operating personnel.

The main problem of such a measuring apparatus consists in preventing deposits of dust in the ray path. Even the finest layers of dust lead to a major falsification of the measurement result. The foils 6 and 7 lying in the ray path are kept clean by the feed of a dust-free gas, especially compressed air, constantly through the nozzles 8 and 9, which gas escapes through the openings 2 and 3 into the conveyor pipe 1. This gas or air current must be so powerful that it prevents even the largest dust particles from penetrating through the openings 2 and 3 into the tube sections 4a, and 5a. The keeping clean of the foils 6 and 7 is additionally favored by the design of the conveyor pipe 1 at the measurement cross-section. The constriction of the conveyor pipe 1 after the style of a Venturi tube in fact has the effect that especially the large dust grains traverse the measurement cross-section in its middle region, where the air velocity reaches the maximum It is naturally favorable for satisfactory measurement results that the conveyor pipe I is installed in a region of the burner conduit where the latter has no major curvatures.

Since the coal dust density in the conveyor pipe 1 is relatively low, the foils 6 and 7 must be made as thin as possible, in the interests of indication sensitivity. However, a certain minimum strength is necessary so that the foil will not be destroyed in the case of pressure surges. For the same reasons of measurement technique, the radioactive emitter, especially Strontium 90, will be covered only with a thin foil. This applies analogously to the radiation receiver, which can be formed, for example, as a B-ionization, chamber with an argon filling.

For safety technical reasons, damage or loss of the radioactive preparation in the case of any faults in the measuring apparatus must be prevented at all costs. In order to preclude all risk, the tube section 4b is monitored by the light barrier as described. If the compressed air supply should fail and at the same time the foil 6 be destroyed, dust enters the tube section 4b, the light barrier responds and an alarm is tripped. Protection against any external corrosive attack can be provided by inserting the slider 17.

The light barrier l8, 19 before the receiver 11 prevents damage to the receiver in the case of a fault. Thus, only economic considerations are decisive for the installation of this light barrier.

The light barriers could be replaced equally by ultrasonic barriers, with similar results.

If the amplified receiver current is used as regulating value, the temperature of the pre-warmed burner air or of the coal-dust-air mixture, which acts as interference value, should expediently be detected and introduced through a calculator circuit into the regulation circuit.

If in boilers with coal-dust firing, all the burner pipes are monitored with the apparatus as described, it is possible to achieve an optimum operating behaviour.

The advantages achievable with the invention become especially prominent when it is a matter of boilers with frequent change of load and liquid slag withdrawal.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations.

What is claimed is:

1. Apparatus for measuring and/0r regulating the dust content of a gas stream, said apparatus comprising a conveyor pipe through which said gas stream is arranged to pass, a pair of tubes extending from the walls of said conveyor pipe and being substantially diametrically opposed, a radiation emitter located in one of said tubes and a receiver located in the other of said tubes, a pair of foils and a pair of nozzles, each of said tubes being divided into two portions by a one of said foils and the portions of each one of said tubes between the said one foil and said conveyor pipe having one of said nozzles extending into said tube, each of said nozzles being adapted to be connected to a compressed gas source.

2. Apparatus as claimed in claim 1, in which said conveyor pipe is narrowed in cross section at the point from which said tubes extend.

3. Apparatus as claimed in claim 1, including a light transmitter on one side of the portion of the tube between one of said foils and said emitter, a light receiver viewing said light transmitter across said tube to provide a light barrier thereacross, an alarm system, and electrical circuitry interconnecting the alarm system with the light receiver whereby failure of said foil resulting in light attenuation in said portion is detected by the light receiver and triggers operation of the alarm.

4. Apparatus as claimed in claim 3, including a slide located in said tube between the emitter and the light barrier, said slide normally being in an inoperative position but being adapted, on activation of said alarm systern, to move to a position in which it cuts off the light barrier and foil from the emitter.

5. Apparatus as claimed in claim 1, including a light transmitter on one side of the portion of the tube between a second of said foils and said receiver, a light receiver viewing the light transmitter across the lastmentioned of said portions to provide a light barrier thereacross, an alarm system, and electrical circuitry interconnecting said alarm system with the light receiver whereby failure of said second foil resulting in attenuation in said last-mentioned portion is detected by the light receiver and triggers operation of the alarm.

6. Apparatus as claimed in claim 1, for use in boiler installations with coal dust firing, said apparatus including regulating means to maintain the ratio of dust to gas in said gas stream substantially constant, an amplifier to amplify current from the receiver, and to operate said regulating means, and circuitry between the amplifier and the regulating means whereby such means are controlled by the amplifier.

7. Apparatus as claimed in claim 6, including temperature sensing means for measuring the temperature of the dust and gas mixture, and means for introducing said temperature as an interference value into said regulating means. 

1. Apparatus for measuring and/or regulating the dust content of a gas stream, said apparatus comprising a conveyor pipe through which said gas stream is arranged to pass, a pair of tubes extending From the walls of said conveyor pipe and being substantially diametrically opposed, a radiation emitter located in one of said tubes and a receiver located in the other of said tubes, a pair of foils and a pair of nozzles, each of said tubes being divided into two portions by a one of said foils and the portions of each one of said tubes between the said one foil and said conveyor pipe having one of said nozzles extending into said tube, each of said nozzles being adapted to be connected to a compressed gas source.
 2. Apparatus as claimed in claim 1, in which said conveyor pipe is narrowed in cross section at the point from which said tubes extend.
 3. Apparatus as claimed in claim 1, including a light transmitter on one side of the portion of the tube between one of said foils and said emitter, a light receiver viewing said light transmitter across said tube to provide a light barrier thereacross, an alarm system, and electrical circuitry interconnecting the alarm system with the light receiver whereby failure of said foil resulting in light attenuation in said portion is detected by the light receiver and triggers operation of the alarm.
 4. Apparatus as claimed in claim 3, including a slide located in said tube between the emitter and the light barrier, said slide normally being in an inoperative position but being adapted, on activation of said alarm system, to move to a position in which it cuts off the light barrier and foil from the emitter.
 5. Apparatus as claimed in claim 1, including a light transmitter on one side of the portion of the tube between a second of said foils and said receiver, a light receiver viewing the light transmitter across the last-mentioned of said portions to provide a light barrier thereacross, an alarm system, and electrical circuitry interconnecting said alarm system with the light receiver whereby failure of said second foil resulting in attenuation in said last-mentioned portion is detected by the light receiver and triggers operation of the alarm.
 6. Apparatus as claimed in claim 1, for use in boiler installations with coal dust firing, said apparatus including regulating means to maintain the ratio of dust to gas in said gas stream substantially constant, an amplifier to amplify current from the receiver, and to operate said regulating means, and circuitry between the amplifier and the regulating means whereby such means are controlled by the amplifier.
 7. Apparatus as claimed in claim 6, including temperature sensing means for measuring the temperature of the dust and gas mixture, and means for introducing said temperature as an interference value into said regulating means. 